1. Field of the Invention
This invention pertains to gas metal arc welding (GMAW), and more particularly to guns used in mig welding.
2. Description of the Prior Art
Mig guns must perform several different functions in order for successful welding to occur. Those functions include directing the weld wire to the workpiece, conducting electric power to the weld wire, and shielding the welding arc from atmospheric air. In addition to the foregoing basic requirements, it is highly desirable that the weld wire be fed to the workpiece at an adjustable rate that suits the particular welding operation at hand. For maximum productivity, it is also necessary that the gun be very comfortable for the operator to maneuver as he directs the weld wire to the workpiece.
To satisfy the foregoing requirements, the gun is connected by a long flexible cable to a wire feeder, which is in close proximity to a welding machine. The welding machine supplies the weld wire, electric power, cooling fluid, and inert shielding gas through the cable to the gun. In some instances, the cable may be as long as 30 feet. Small diameter aluminum weld wire, as is typically used when welding aluminum workpieces, has insufficient column strength to be satisfactorily pushed for such long distances to the gun. Accordingly, it is known to provide mig guns with a feed mechanism that pulls the weld wire at the same time the wire feeder attached to the welding machine is pushing the weld wire.
The gun feed mechanism is contained in a handle that is held by the operator. There is a head tube on the end of the handle opposite the flexible cable. A diffuser is joined to the free end of the head tube. A contact tip is connected to the diffuser. The weld wire is guided by a liner that extends from the handle to the diffuser. From the diffuser, the weld wire passes through the contact tip, from which it emerges under the impetus of the feed mechanism.
An example of a prior mig gun is manufactured by M. K. Products, Inc., of Irvine, Calif., under the trademark Cobra. That gun has a long straight handle that contains a weld wire feed mechanism. The feed mechanism includes a motor having an axial center line inside and parallel to the handle longitudinal axis. The motor drives a feed roller that, in conjunction with an undriven idler roll, pulls the weld wire from the wire feeder of the welding machine. The axes of rotation of the feed rollers are perpendicular to the motor axial center line. The gun feed mechanism is adjustable by a non-graduated knob on a side of the handle. The non-graduated knob enables the operator to control the weld wire feed rate through a range from zero to a maximum over three turns of the knob.
The prior Cobra gun has two disadvantages. First, the straight handle makes the gun rather cumbersome to maneuver by the operator through the multiplicity of spacial positions encountered when welding various workpieces. Second, the weld wire feed control knob is located where it is awkward to adjust by a left-handed operator and, being non-graduated, it is almost impossible to determine the preset position. The operator must either transfer the gun to his right hand to adjust the knob, or he must turn the gun in his left hand so the knob is accessible to his right hand.
An example of another prior mig gun with a weld wire feed mechanism may be seen in U.S. Pat. No. 5,728,995. The gun of that patent is in the general configuration of a pistol. The operator holds an electric motor that is at a right angle to the longitudinal axis of the gun. The motor axial centerline is parallel to the axes of rotation of feed rollers that pull the weld wire. A head tube curves away from the handle at the handle downstream end. The pistol-type gun is also awkward to maneuver into some of the numerous spacial positions encountered in welding operations.
As mentioned, it is vital that the mig gun adequately shield the welding arc from the atmosphere. For that purpose, inert gas is supplied to prior guns from the welding machine through the flexible cable. The inert gas is directed through the gun head tube to the interior of the diffuser. The gas flows from the diffuser to a nozzle that surrounds the contact tip. The gas then flows out the nozzle and surrounds the contact tip and the weld wire emerging from it. The gas thus shields the weld wire and the welding arc from the atmosphere.
Despite the widespread use and general acceptance of the prior designs of diffusers and nozzles, they nevertheless are not completely acceptable. Specifically, a sooty deposit has been noticed from some welding operations on aluminum workpieces that use aluminum weld wire. The soot is carbon residue produced in the welding arc. The source of the carbon is a boundary layer of air that surrounds the weld wire inside the clearance holes in the liner and the contact tip. Although the spaces between the weld wire and the liner and contact tip clearance holes are very small, they nevertheless are sufficient to enable some air to pass inside the inert gas shield from the nozzle and thus be present at the welding arc.
Accordingly, it is desirable that improvements be made to GMAW guns.